Note: Descriptions are shown in the official language in which they were submitted.
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POWER TONG WITH LINEAR LAMMING SURFACES
FIELD OF THE INVENTION
The present invention relates in general to power tongs for gripping oilfield
tubulars to
S facilitate make-up or break-out of threaded connections between tubulars. In
particular, the
invention relates to pivoting j aw power tongs having rotary gears with
improved camming
surface geometry.
BACKGROUND OF THE INVENTION
Power tongs are well known in the field of drilling and servicing oil and gas
wells.
Drill pipe and production tubing are typically provided in the form of round
steel pipe
(commonly referred to as tubulars) with threaded ends for connecting tubulars
into a drill string
or a production string, depending on the operation being conducted. The term
"make-up" is
commonly used to refer to the process of connecting tubulars to each other
(i.e., "making up" a
threaded connection), and the term "break-out" refers to the process of
disconnecting tubulars
(i.e., "breaking out" a threaded connection). Well drilling and well servicing
involve both
make-up and break-out functions, for a variety of purposes well known in the
field.
Make-up or break-out of a threaded joint requires that the tubular on each
side of the
joint be firmly gripped so that the tubulars can be contra-rotated relative to
each other, either
clockwise or counterclockwise, to make up or break out the joint as desired.
This gripping
function is commonly carned out using a power tong on each of the tubulars.
Power tongs
typically have either sliding jaw assemblies or pivoting jaw assemblies, and
the present
invention is particularly referable to the pivoting jaw type. There are
numerous known types or
models of pivoting jaw power tongs, but they generally have the common
features of a partial-
circle (or "C-shaped") rotary gear, the internal surface of which defines a
camming surface, and
a jaw assembly disposed inside the rotary gear and having two or more cam
followers that ride
against the camming surface of the rotary gear. The cam followers may be in
the form of
rollers which turn around suitable axles or pivot pins, or they may be formed
integrally with the
jaws. The jaw assembly has several (typically four) dies -- i.e., elements
which are toothed or
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otherwise adapted for grippingly engaging the circumferential outer surface of
a tubular
member by effectively biting into the steel surface of the tubular when forced
against the
tubular. The geometry of the camming surface is adapted such that when the
rotary gear is
rotated around the jaw assembly, either clockwise or counterclockwise away
from a neutral
position, the dies are urged into gripping contact with the outer surface of
the tubular. When
the tubulars on each side of the joint have been thus engaged by respective
power tongs, the
tongs may be rotated relative to each other in the desired mode, thus making
up or breaking out
the joint as desired.
One example of a prior art pivoting jaw power tong is disclosed in Canadian
Patent No.
1,125,737 issued on June 15, 1982 to Farr et al. (and corresponding to U.S.
Patent No.
4,350,062). As with typical pivoting jaw power tongs, the camming surface of
the Farr device
includes a pair of opposed recesses (or neutral zones) such that when the
rotary gear is rotated
to a neutral position wherein each cam follower has moved into one of the
recesses, the jaws
spread apart so as to allow the jaws to receive a tubular. On either side of
each recess, the
camming surface has a circularly-curved primary camming surface. These primary
camming
surfaces are configured such that when the rotary gear is rotated in either
direction away from
the neutral position, each jaw is rotated inward. As rotation of the rotary
gear increases, the
jaws close on the tubular, causing the dies to bite into the tubular. When the
tubular is firmly
gripped by the dies, the tubular can be rotated so as to be connected to or
disconnected from (as
the case may be) another tubular.
The primary camming surfaces of the Farr device have different curvature radii
on
either side of each recess, and this is considered to have certain advantages
over typical prior
art pivoting jaw power tongs in which the same curvature radius is used for
all of the primary
camming surfaces. However, it has been observed that power tongs with circular
primary
caroming surfaces are prone to reduced effectiveness as the dies, pins,
rollers, and/or caroming
surfaces become worn. In such circumstances, the force with which the dies are
urged against
the surface of the tubular is not uniform, so the dies grip the tubular with
variable effectiveness,
and in the worst case a die may grip the tubular with little or no
effectiveness at all. In such
cases only three of the dies will be effectively gripping the tubular instead
of four, and this
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condition tends to causing warping and/or marking of the tubular. This tends
to be a particular
problem for the dies located near the pivot points of the jaws.
For the foregoing reasons, there is a need for improved pivoting jaw power
tongs
having enhanced capability for reliable and effective gripping engagement of
tubular members
in cases where dies, pins, rollers, and/or caroming surfaces are worn. The
present invention is
directed to this need.
BRIEF SUMMARY OF THE INVENTION
The present invention addresses this need by providing a pivoting jaw power
tong in
which the primary caroming surfaces of rotary gear have a novel geometry. Each
primary
caroming surface has a substantially linear configuration, rather than a
circularly-curved
configuration. More specifically, each primary caroming surface is oriented so
as to form an
acute angle with a radial line extending from the rotary gear to the point
where the primary
caroming surface meets its corresponding neutral recess. By virtue of this
geometric
configuration, the radial distance to a point on any of the primary caroming
surfaces reduces, in
substantially linear fashion, with increased distance away from the neutral
recess. Therefore,
increased rotation of the ring gear in either direction away from the neutral
position will cause
both jaws to rotate further inward, thus increasing the force that the dies on
the free ends of the
jaws will exert on a tubular being engaged by the apparatus.
The inventor has discovered that when using a power tong having such linearly-
configured primary caroming surfaces, the dies will engage the tubular with
considerably
increased uniformity and effectiveness, even when the dies, pins, cam
followers (e.g., rollers),
and/or caroming surfaces are worn. In prior art power tongs with curved
caroming surfaces
(such as in the Farr reference), there is a relatively small "sweet spot" or
optimal contact zone
on the caroming surface corresponding to each cam follower such that each die
will exert
maximum gripping force on the tubular when the cam followers are at their
corresponding
sweet spots. This works well when the apparatus is new, without any wear to
the various
components. All of the cam followers will hit their sweet spots at the same
time (i.e., when the
rotary gear is in a specific optimal position), because the distance from the
rotary gear's center
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of rotation to the sweet spot is the same for all of the cam followers, the
distance from the
center of rotation to the face of the cam followers is constant, and the
distance from the center
of rotation to the die contact surfaces is constant.
Continued use of the power tong inevitably results in wear to the components,
however,
and a certain amount of "play" develops in the mechanism. This causes changes
in the
geometrical relationship between the cam followers, dies, and/or caroming
surfaces, such that
the cam followers can no longer hit their sweet spots at the same time. In
effect, one or more of
the sweet spots become shifted to a different position on the caroming surface
because of the
wear, and the geometric relationship between the sweet spots no longer
coincides precisely
with the geometric relationship between the cam followers. Even small amounts
of play can
thus result in reduced gripping force being applied to the tubular at one or
more of the dies,
such that the tubular is not gripped uniformly.
This undesirable condition cannot be effectively remedied by further rotation
of the
rotary gear, because the tangential angle between the cam followers and the
caroming surfaces
(which may be referred to as the "tangential contact angle") changes as the
cam followers move
away from their sweet spots or optimal contact zones on the caroming surfaces,
due to the fact
that the caroming surfaces are curved. However, when substantially linear
caroming surfaces
are used, as in the present invention, the tangential contact angle will be
substantially the same
for all cam followers regardless of the position of the rotary gear, and will
not be materially
altered by normal operational wear to the various components of the power
tong.
In the present invention, the linear caroming surfaces are oriented such that
the radial
distance from the center of rotation to the caroming surface decreases in
substantially linear
fashion as the caroming surfaces propagate away from the neutral recesses in
the caroming
surfaces. By virtue of this caroming surface geometry, rotation of the rotary
gear in either
direction away from the neutral position results in a linearly progressive
reduction of the
distance from the center of rotation to the points where the cam followers
contact the caroming
surfaces, with the rate of reduction varying in proportion to the angular
displacement of the
rotary gear, regardless of how far the cam followers may be displaced away
from the neutral
recesses.
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The inventor has found that the use of such linear camming surfaces results in
a much
larger sweet spot corresponding to each cam follower. This camming surface
geometry allows
the power tong to automatically adjust for wear in the mechanism such that the
contact force
between the cam followers and the camming surfaces - and, therefore, the
gripping force
applied by the dies to the tubular - will be substantially constant at all
locations.
Accordingly, in one aspect the present invention is a power tong having:
(a) a gear housing defining a central space, and a perimeter opening into said
space; and
(b) a pair of opposing jaw members disposed within said central space, each
jaw member
having:
b.l a pivot end, a free end, an inner side, and an outer side, with said pivot
end
pivotably mounted to the gear housing, and said free end oriented toward said
perimeter opening;
b.2 a pair of dies associated with said inner side; and
b.3 a cam follower associated with said outer side;
(c) a rotary gear rotatably mounted within the gear housing, and having:
c. l a circular perimeter with a plurality of gear teeth;
c.2 an inner surface defining a central space large enough to enclose said jaw
members; and
c.3 a throat opening in said perimeter;
wherein said inner surface defines:
(d) a pair of opposed neutral recesses; and
(e) a first pair of opposing primary camming surfaces, each extending
substantially linearly
in a first direction away from an associated one of the recesses;
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and wherein the radial distance from the axis of rotation of the rotary gear
to a point on
any primary camming surface decreases substantially linearly with increased
distance
from the associated recess.
In the preferred embodiment, each cam follower will be a roller, rotatably
mounted to a
corresponding jaw member.
In a second aspect, the present invention is a rotary gear substantially as
described
above, for use in a pivoting jaw power tong.
In an alternative embodiment of the invention, only two of the primary camming
surfaces are of linear orientation. In this embodiment, the two primary
camming surfaces in
question will be diametrically opposed, such that each of them will be engaged
by one of the
cam followers when the rotary gear is rotated in a particular direction; in
other words, they will
both be disposed either clockwise of the neutral recesses, or counterclockwise
of the recesses.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the present invention will now be described with reference to
the
accompanying figures, in which numerical references denote like parts, and in
which:
FIGURE 1 is an isometric view of a power tong in accordance with an
embodiment of the present invention, shown with the rotary gear in the neutral
position such that a tubular can pass through the throat opening when the
hinged
doors have been opened.
FIGURE 2 is a perspective view of the rotary gear of a power tong in
accordance with one embodiment of the invention.
FIGURE 3 is a plan view of the rotary gear of Figure 2.
FIGURE 4 is an enlarged plan view of the rotary gear of Figure 2, illustrating
the geometric configuration of the camming surfaces.
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FIGURE 5 is a plan view of the rotary gear and pivoting jaws of a power tong
in accordance with one embodiment of the invention, shown with the rotary gear
in the open position in which a tubular can pass through the throat of the
rotary
gear and into position between the pivoting jaws.
FIGURE 6 is a plan view of the rotary gear and pivoting jaws as in Figure 5,
shown with the rotary gear rotated counterclockwise from the neutral position,
with a tubular positioned inside the pivoting jaws, and with the jaws' dies
beginning to engage and grip the tubular.
FIGURE 7 is a plan view of the rotary gear and pivoting jaws as in Figure 5,
shown with the rotary gear rotated further counterclockwise, with the front
pair
of dies securely engaging and gripping the tubular.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Figure 1 generally illustrates an assembled power tong 10 in accordance with
one
embodiment of the present invention. With the exception of the configuration
of the camming
surfaces of the rotary gear (which is not visible in Figure 1), the
construction of power tong 10
is largely similar to known power tongs. A generally-C-shaped gear housing 12
has doors 14
which can be swung open about hinge points 18 using handles 16 (as indicated
by the broken
arrows in Figure 1) so as to provide an opening into a central space 19 within
gear housing 12.
A pair of jaw members 20 (typically of generally arcuate shape) are pivotably
mounted within
gear housing 12. As shown in Figure 5, each jaw member 20 has a pivot end 20A,
a free end
20B, an inner side 20C disposed toward central space 19, and an outer side
20D. The pivot
end 20A of each jaw member 20 is pivotably mounted to gear housing 12 by means
of a pivot
pin 22, at a point opposite the opening into central space 19. Dies 30, for
grippingly engaging a
tubular, are mounted on the inner sides 20C of each jaw member 20 near each
end thereof.
Additional features of jaw members 20 are shown in Figures S, 6, and 7, and
described in
greater detail further on in this specification.
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Disposed within gear housing 12 (but not shown in Figure 1) is a generally C-
shaped
rotary gear 40, exemplary embodiments of which are is illustrated in Figures 2-
7. Rotary gear
40 has a circular perimeter with a plurality of gear teeth 41. Rotary gear 40
also has an inner
surface 42 which encloses a central space 48 of sufficient size to enclose jaw
members 20
without interference. The perimeter of rotary gear 40 is interrupted by a
throat opening 46
which provides access to central space 48. Rotary gear 40 is mounted within
gear housing 12
so as to surround jaw members 20 (as best seen in Figures 5-7), and so as to
be rotatable within
gear housing 12 about center axis C of rotary gear 40. The power tong 10
includes means for
rotating rotary gear 40, and such means may be of any suitable type well known
in the field of
the invention. For exemplary purposes, Figure 1 illustrates power tong 10 with
hydraulic
actuation means 100, comprising a hydraulic motor 110 which rotates a pinion
gear (not
shown) that engages gear teeth 41 so as to rotate rotary gear 40 clockwise or
counterclockwise
as desired, by means of hydraulic valve control levers 112. Hydraulic lines
114 lead from
hydraulic actuation means 100 to a hydraulic pump (not shown) associated with
the drilling rig
or service rig on which power tong 10 is being used. Figure 1 also illustrates
a lifting ring 120
of a type that may be used for suspending power tong 10 from the rig's hoist.
The three-dimensional configuration of rotary gear 40 is illustrated in Figure
2. As
shown in plan view in Figure 3, inner surface 42 is of a generally circular
configuration, but
includes several geometrically distinct portions. If rotary gear 40 as
illustrated in Figure 3 is
analogized to a clock face, with throat opening 46 at approximately six
o'clock, a first neutral
recess 43A is formed in inner surface 42 at approximately nine o'clock, and a
second neutral
recess 43B is formed in inner surface 42 at approximately three o'clock. The
purpose of these
neutral recesses will be explained later in this document.
First neutral recess 43A is contiguous with inner surface 42 at points W and
X, and
second neutral recess 43B is contiguous with inner surface 42 at points Y and
Z. Inner surface
42 includes substantially linear (i.e., substantially planar) primary caroming
surfaces 44W,
44X, 44Y, and 44Z which propagate away from transition points W, X, Y, and Z
respectively,
as shown in Figure 3. Primary caroming surfaces 44W, 44X, 44Y, and 44Z are
indicated in
Figure 3 as having lengths LW, Lx, LY, and Lz respectively. The magnitude of
these lengths
will be dependent on the particular requirements of a given power tong 10.
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The geometric characteristics of primary caroming surfaces 44W, 44X, 44Y, and
44Z
are illustrated in Figure 4. A radial line R extending from center axis C to
transition point W,
X, Y, or Z will form an acute angle (AW, Ax, AY, or Az) with the corresponding
primary
caroming surface 44W, 44X, 44Y, or 44Z. By virtue of this geometric
characteristic, the radial
distance from center axis C to a point on a given primary caroming surface
decreases in
substantially linear fashion according to the distance away from the
corresponding transition
point. Acute angles AW, Ax, AY, or AZ will typically be between eighty and
ninety degrees, but
the precise magnitude of these angles will be determined to suit the
particular requirements of a
given application (including, for example, the size of tubular T on which the
power tong 10 is
to be used).
Figures 5, 6, and 7 illustrate rotary gear 40 with jaw members 20 disposed
within
central space 48, and within gear housing 12 (the components of which are
omitted from
Figures S, 6, and 7 for clarity). As previously mentioned, the pivot end 20A
of each j aw
member 20 pivots about a pivot pin 22 mounted to gear housing 12 at a point
generally
opposite throat opening 46. Each jaw member 20 has a cam-following element (or
cam
follower) 24 associated with outer side 20D. In the embodiments shown in
Figures 5, 6, and 7,
cam followers 24 are provided in the form of protuberances formed integrally
with jaw
members 20. Alternatively, cam followers 24 may be in the form of rollers
rotatably mounted
to their corresponding jaw members 20 using suitable axles or pivot pins. In
any event, jaw
members 20, cam followers 24, inner surface 42, and neutral recesses 43A and
43B are
configured and arranged such that jaw members 20 can pivot outward into an
open position (as
illustrated in Figure 5) in which each cam follower 24 is disposed within a
corresponding
neutral recess (43A or 43B), and in which a tubular T can pass through throat
opening 46 of
rotary gear 40 into central space 48, and so as to be substantially concentric
with center axis C
of rotary gear 40.
The basic operation of the power tong 10 may be understood with reference to
Figures 6
and 7. In Figure 6, with a tubular T positioned between j aw members 20,
rotary gear 40 has
been rotated counterclockwise (as indicated by the curved arrows) relative to
jaw members 20
(and relative to gear housing 12). The rotation of rotary gear 40 has forced
cam followers 24
out of their corresponding neutral recesses 43A and 43B, such that they engage
opposing
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primary camming surfaces 44W and 44Z. As a result, the free ends 20B of jaw
members 20
have rotated inward to the point that dies 30A and 30B have begun to engage
the cylindrical
outer surface of tubular T. Because primary camming surfaces 44W and 44Z are
of linear (or
planar) configuration as previously described, further counterclockwise
rotation of rotary gear
S 40 causes further inward rotation of jaw members 20 such that dies 30A and
30B bite into
tubular T as shown in Figure 7. Tubular T is thus securely gripped by jaw
members 20,
thereby facilitating rotation of tubular T relative to an adjoining tubular.
In similar fashion, clockwise rotation of rotary gear 40 (from the open
position) would
cause cam followers 24 to engage opposing linear primary camming surfaces 44x
and 44Y.
In the embodiment described above, inner surface 42 of rotary gear 40 defines
linear
primary camming surfaces adjacent to each neutral recess. Alternative
embodiments may have
only one opposing pair of linear primary camming surfaces (i.e., 44W and 44Z,
or 44x and 44Y),
with the other opposing pair of camming surfaces being of a different
configuration (e.g.,
curved).
It will be readily appreciated by those skilled in the art that various
modifications of the
present invention may be devised without departing from the essential concept
of the invention,
and all such modifications are intended to be included in the scope of the
claims appended
hereto.
In this patent document, the word "comprising" is used in its non-limiting
sense to mean
that items following that word are included, but items not specifically
mentioned are not
excluded. A reference to an element by the indefinite article "a" does not
exclude the possibility
that more than one of the element is present, unless the context clearly
requires that there be
one and only one such element.
